CHICAGO (AP) _ Parking ticket scofflaws are lining up by the hundreds to take advantage of a the city's bid to reap millions of overdue dollars by slashing fines in half.

The city says it's simple: sign up by midnight Thursday or face the dreaded ''Denver boot,'' an auto immobilizer guaranteed to make motorists think twice before forgetting to plunk some change in the parking meter.

So far, more than 100,000 people and businesses have called or written the city or streamed into the Revenue Department and Traffic Court, agreeing to pay about $5.5 million for any tickets issued between 1980 and last September.

Commonwealth Edison Co., a utility serving Chicago and other parts of northeastern Illinois, paid $17,000.

''You know what it looked like in the old days when they had a good first- run movie? The lines were out the door and around the corner. Well, that's what we've got here,'' said Cook County sheriff's Deputy Art Lapointe.

The line of scofflaws has stretched through the Traffic Court corridor and out the revolving door on LaSalle Street for the past two weeks.

Motorists mail or bring in their tickets, agree to pay half and the names are scratched from the city's hit list. Many of the violators failed to feed the meter, but others have tickets for parking in restricted areas.

Patrick Quinn, the city's revenue director, said Chicago is owed about $70 million from a seven-year backlog of 7 million unpaid tickets.

''People are coming out of the woodwork, and not just the people, but businesses, too,'' Quinn said. ''Historically, the standard of conduct for the people of Chicago was 'Get away with what you can.' Well, that's coming to an end.''

City officials said they believe the program, which began Feb. 17, was the most effective way to get people to pay.

By summer, Quinn said the city will begin using the metal ''Denver boot'' on cars whose owners have 10 or more unpaid tickets. Cars would remain immobilized until the driver settles the fines.

''It's a great deal,'' said Henry Hoppe, pausing to answer questions Tuesday as sheriff's police urged him to move ahead in the long line at Traffic Court.

''Once it's done, it's off your head. Isn't it easier to stand in line for an hour and be through with it?'' he asked.

Hoppe had only four tickets, a $50 fine, but Victor Torenzo was another story.

Torenzo, 42, said he wouldn't know what the price tag would be on his 130 tickets until he got to the front of the line.

''I park in the wrong places because there are few legal places to put all the cars in this city,'' he said.

''I've thought of methods to take off the 'Denver boot,' but then that would be destruction of public property,'' he said. ''It's cheaper just to pay the fines.''